The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In some application circuits, an external resistor is connected to a device to program digital information in the device. The external resistor may be used to set an address or specify data to configure a programmable function (either analog or digital). For example only, the programmed information may correspond to an address of a device, a threshold of an internal comparator, or other programmed information.
Some circuits supply a constant current to the external resistor and read a corresponding voltage drop using an analog to digital converter (ADC). FIG. 1 shows an example of a detector circuit 10 including an external resistor 20 that is connected to a current source 34, which supplies a constant current i. An analog to digital converter (ADC) 38 receives a voltage Vin and generates an n-bit digital code. The ADC 38 and the current source 34 may be connected to reference voltages Vref1 and Vref2, which may be the same or different. The tolerance of the external resistor 20 is:
                    R                  K          +          1                    -              R        K                    R      K        =      1          2      n      